CN108023568B

CN108023568B - Filter device, multiplexer, high-frequency front-end circuit and communication device

Info

Publication number: CN108023568B
Application number: CN201711020437.1A
Authority: CN
Inventors: 加藤雅则; 木户俊介
Original assignee: Murata Manufacturing Co Ltd
Current assignee: Murata Manufacturing Co Ltd
Priority date: 2016-10-31
Filing date: 2017-10-27
Publication date: 2021-06-25
Anticipated expiration: 2037-10-27
Also published as: US20180123547A1; US20190173448A1; CN108023568A; US10250214B2; US10727805B2

Abstract

The invention relates to a filter device, a multiplexer, a high-frequency front-end circuit and a communication device, which can realize the filter characteristic with small loss. The filter is provided with series arm resonators (s1) and (s2) connected in series between an input/output terminal (11m) and an input/output terminal (11n), a parallel arm resonator (p1) connected between a series arm between the series arm resonators and the ground, an inductor connected in parallel with the series arm resonators, and a matching circuit connected between the series arm resonator (s2) and the input/output terminal (11n), wherein the series arm resonator and the parallel arm resonator constitute a pass band of the band-pass filter, the series arm resonators (s1) and (s2) and the inductor constitute an LC resonance circuit, the anti-resonance frequencies of the series arm resonators (s1) and (s2) and the resonance frequency of the parallel arm resonator are located in the pass band of the LC resonance circuit, and the resonance frequency of the LC resonance circuit is lower than that of the parallel arm resonators.

Description

Filter device, multiplexer, high-frequency front-end circuit and communication device

Technical Field

The present invention relates to a filter device having a resonator, a multiplexer (multiplexer), a high frequency front end (front) circuit, and a communication device.

Background

Conventionally, a ladder filter device using an elastic wave resonator has been proposed. For example, a filter device including two series arm resonators, three parallel arm resonators, and an inductor arranged so as to straddle the two series arm resonators is disclosed (for example, see patent document 1). In this filter device, a low-pass filter (LC resonant circuit) is configured by an inductor and two series arm resonators. In addition, the resonance frequencies of two series arm resonators or three parallel arm resonators are located in the attenuation band of the low-pass filter. In this way, the sharp attenuation pole caused by the harmonic oscillator overlaps the attenuation band of the low-pass filter, thereby improving the attenuation characteristics.

Patent document 1: japanese patent No. 5088416

However, in the above-described conventional configuration, since the attenuation pole caused by the low-pass filter (LC resonant circuit) overlaps with the steep attenuation pole caused by the resonator, there is a problem that the loss of the pass band increases.

Disclosure of Invention

The present invention has been made to solve the above-described problems, and an object thereof is to provide a filter device, a multiplexer, a high-frequency front-end circuit, and a communication device that can realize a filter characteristic with a small loss.

In order to achieve the above object, a filter device according to an aspect of the present invention includes: a first series arm resonator provided on a first terminal side and a second series arm resonator provided on a second terminal side, the first series arm resonator being connected in series between the first terminal and the second terminal; a parallel arm resonator connected between a series arm between the first series arm resonator and the second series arm resonator and a ground; a first inductor connected in parallel to the first series arm resonator and the second series arm resonator; and a matching circuit connected between the second series arm resonator and a second terminal, or connected between the first series arm resonator and the first terminal, wherein the first series arm resonator, the second series arm resonator, and the parallel arm resonator constitute a passband of a band pass filter, the first series arm resonator, the second series arm resonator, and a first inductor constitute an LC resonance circuit, wherein anti-resonance frequencies of the first series arm resonator and the second series arm resonator, and a resonance frequency of the parallel arm resonator are located in a passband of the LC resonance circuit, and a resonance frequency of the LC resonance circuit is lower than a resonance frequency of the parallel arm resonator.

Accordingly, the two series arm resonators and the first inductor constitute an LC resonant circuit having a wide passband. When the anti-resonance frequency of each of the two series arm resonators and the resonance frequency of the parallel arm resonator are located in the passband of the LC resonance circuit, each resonator operates as a notch filter, and the passband of the LC resonance circuit is locally attenuated. At this time, since the anti-resonance frequency of each of the two series arm resonators is higher than the resonance frequency of the parallel arm resonator, the parallel arm resonator forms an attenuation slope on the low frequency side of the passband of the filter device, and the two series arm resonators form an attenuation slope on the high frequency side of the passband. Therefore, the anti-resonance frequency of each of the two series arm resonators is separated from the resonance frequency of the parallel arm resonator, and the passband can be made wide. In addition, the loss of the passband can be reduced by the matching circuit. This makes it possible to realize a bandpass filter characteristic having a wide passband and a low loss.

The resonance frequency of the parallel arm resonator may be lower than the resonance frequency of each of the first series arm resonator and the second series arm resonator.

The matching circuit may be a second inductor connected between the first terminal and the second terminal and ground.

This enables the matching circuit to function as a filter for attenuating a low frequency band (699 MHz-960), for example.

The matching circuit may be a third inductor connected in series between the first terminal and the second terminal.

This enables the matching circuit to function as a filter for attenuating a 5GHz band, for example.

The parallel arm resonator, the first series arm resonator, and the second series arm resonator may be each configured by a substrate having a piezoelectric layer, and an IDT electrode formed on the substrate, and a piezoelectric material constituting the piezoelectric layer of the parallel arm resonator may be different from a piezoelectric material constituting the piezoelectric layer of the first series arm resonator and the piezoelectric layer of the second series arm resonator.

For example, when the piezoelectric materials are the same, an unnecessary wave (bulk wave) which becomes an important factor of the material may be generated, and the loss of the passband becomes large.

The parallel arm resonator, the first series arm resonator, and the second series arm resonator may each be configured from a substrate having a piezoelectric layer, and an IDT electrode formed on the substrate, and the cut angle of the piezoelectric layer configuring the parallel arm resonator may be different from the cut angle of the piezoelectric layer configuring the first series arm resonator and the second series arm resonator.

For example, when the respective cut angles are the same, there is a possibility that an unnecessary wave (bulk wave) whose cut angle becomes an important factor is generated, and the loss of the passband becomes large.

At least one of the parallel arm Resonator, the first series arm Resonator, and the second series arm Resonator may be a BAW (Bulk Acoustic Wave) Resonator or an FBAR (Film Bulk Acoustic Resonator).

A multiplexer according to an aspect of the present invention includes a plurality of filters including at least one filter device described above, and an input terminal or an output terminal of each of the plurality of filters is directly or indirectly connected to a common terminal.

Thus, a multiplexer capable of realizing a filter characteristic with a small loss can be provided.

In addition, the plurality of filters may be two filters.

Thus, a duplexer capable of realizing a filter characteristic with a small loss can be provided.

The plurality of filters may be three filters.

Thus, a triplexer capable of realizing a filter characteristic with a small loss can be provided.

The plurality of filters may be four filters.

Thus, a quadruplex device capable of realizing a filter characteristic with a small loss can be provided.

The plurality of filters may include another filter connected to the first terminal and having a passband at a different frequency from the filter device, and the resonance frequency of the LC resonance circuit may be located in a passband of the other filter.

This can suppress deterioration of the transmission characteristics of the other filters.

The resonance frequency of the LC resonance circuit may be located on a lower frequency side than the center frequency of the passband of the other filter.

Accordingly, the resonance frequency of the LC resonant circuit is located on the lower frequency side of the passband of the other filter than the center frequency, and the attenuation pole by the LC resonant circuit is located at a far position from the passband of the filter device. Therefore, the passband is less susceptible to the attenuation pole by the LC resonant circuit, and the loss on the low frequency side of the passband can be further suppressed from increasing.

In addition, the passband of the filter device can be adapted to the high band (2300-.

Accordingly, a filter characteristic with a small loss can be realized over the entire high frequency band (2300-. In addition, the loss of the middle frequency band (1710- & 2200MHz) of other filters can be suppressed.

The plurality of filters may include a low-pass filter. For example, the passband of the low pass filter may also be adapted to the low band (699-960 MHz). For example, the low-pass filter may be an LC filter.

Accordingly, the loss at the low band (699-960 MHz) of the low-pass filter can be suppressed.

In addition, the multiplexer may simultaneously transmit and receive signals of a plurality of frequency bands corresponding to the respective filters.

This can support Carrier Aggregation (CA).

A high-frequency front-end circuit according to an aspect of the present invention includes the multiplexer and a switch connected to the multiplexer.

Thus, a high-frequency front-end circuit having a switch that can realize a filter characteristic with a small loss can be provided.

A high-frequency front-end circuit according to an aspect of the present invention includes the multiplexer and an amplifier circuit connected to the multiplexer.

Thus, a high-frequency front-end circuit having an amplifier circuit that can realize a filter characteristic with a small loss can be provided.

A communication device according to an aspect of the present invention includes an RF signal processing circuit that processes a high-frequency signal transmitted and received by an antenna element, and the high-frequency front-end circuit that transmits the high-frequency signal between the antenna element and the RF signal processing circuit.

Thus, a communication device capable of realizing a filter characteristic with a small loss can be provided.

According to the filter device, the multiplexer, the high-frequency front-end circuit, and the communication device of the present invention, a filter characteristic with a small loss can be realized.

Drawings

Fig. 1 is a circuit configuration diagram of a filter according to embodiment 1.

Fig. 2 is a diagram schematically showing the structure of a resonator in embodiment 1.

Fig. 3 is a graph showing the filter characteristics of the bandpass filter according to embodiment 1.

Fig. 4 is a graph showing the filter characteristics of the filter according to embodiment 1.

Fig. 5 is a circuit configuration diagram of the filter according to comparative example 1.

Fig. 6 is a graph showing filter characteristics of the filter according to embodiment 1 and the filter according to comparative example 1.

Fig. 7 is a graph showing third-order intermodulation distortion characteristics of the filter according to embodiment 1 and the filter according to comparative example 1.

Fig. 8A is a circuit configuration diagram showing an example of the matching circuit according to embodiment 1.

Fig. 8B is a circuit configuration diagram showing an example of the matching circuit according to embodiment 1.

Fig. 8C is a circuit configuration diagram showing an example of the matching circuit according to embodiment 1.

Fig. 8D is a circuit configuration diagram showing an example of the matching circuit according to embodiment 1.

Fig. 8E is a circuit configuration diagram showing an example of the matching circuit according to embodiment 1.

Fig. 8F is a circuit configuration diagram showing an example of the matching circuit according to embodiment 1.

Fig. 8G is a circuit configuration diagram showing an example of the matching circuit according to embodiment 1.

Fig. 8H is a circuit configuration diagram showing an example of the matching circuit according to embodiment 1.

Fig. 8I is a circuit configuration diagram showing an example of the matching circuit according to embodiment 1.

Fig. 9 is a graph showing filter characteristics of the filter according to example 1 and the filter according to comparative example 2.

Fig. 10 is a graph showing resonator characteristics of the parallel arm resonator according to example 1 and the parallel arm resonator according to comparative example 2.

Fig. 11 is a configuration diagram of a multiplexer and its peripheral circuits according to embodiment 2.

Fig. 12A is a graph showing the passing characteristics of the signal path corresponding to the high frequency band in the multiplexer according to embodiment 2.

Fig. 12B is a graph showing the passing characteristics of the signal path corresponding to the intermediate frequency band in the multiplexer according to embodiment 2.

Fig. 12C is a graph showing the passing characteristics of the signal path corresponding to the low band in the multiplexer according to embodiment 2.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to examples and drawings. The embodiments described below are all illustrative including formulae or specific examples. The numerical values, shapes, materials, constituent elements, arrangement of constituent elements, connection modes, and the like shown in the following embodiments are examples. In the drawings, the same reference numerals are given to substantially the same components, and redundant description may be omitted or simplified.

(embodiment mode 1)

[1. Circuit configuration of Filter ]

Fig. 1 is a circuit configuration diagram of a filter 10 according to embodiment 1.

The filter 10 is a filter device disposed in a front (front) section of a mobile phone corresponding to a multi-mode/multi-band, for example. The filter 10 is a Band-pass filter that is built in a mobile phone that is compatible with multiple bands in accordance with a communication standard such as LTE (Long Term Evolution) and filters a high-frequency signal in a predetermined Band (Band), for example.

As shown in the figure, the filter 10 includes a series arm resonator s1 (first series arm resonator) and a series arm resonator s2 (second series arm resonator), a parallel arm resonator p1, an inductor L1, and a matching circuit 14.

The series arm resonators s1 and s2 are connected in series between the input/output terminal 11m (first terminal) and the input/output terminal 11n (second terminal). That is, the series arm resonators s1 and s2 are resonators connected in series between the input/output terminal 11m and the input/output terminal 11 n. For example, the input/output terminal 11m is an input terminal to which a high-frequency signal is input, and the input/output terminal 11n is an output terminal from which a high-frequency signal is output. The series arm resonator s1 is provided on the input/output terminal 11m side, and the series arm resonator s2 is provided on the input/output terminal 11n side.

The parallel arm resonator p1 is connected between the series arm (node x1 shown in fig. 1) between the series arm resonator s1 and the series arm resonator s2 and ground (reference terminal). That is, the parallel arm resonator p1 is a resonator of a parallel arm provided to connect the node x1 on the series arm to ground.

For convenience, a singular point (ideally, a point at which the impedance is 0) at which the impedance of the resonator is extremely small is referred to as a "resonance point", and the frequency thereof is referred to as a "resonance frequency". In addition, a singular point where the impedance is extremely large (ideally, a point where the impedance is infinite) is referred to as an "antiresonance point", and the frequency thereof is referred to as an "antiresonance frequency".

The series arm resonators s1 and s2 and the parallel arm Resonator p1 are elastic Wave resonators having a resonance point and an anti-resonance point, and are each composed of a Surface Acoustic Wave (SAW) Resonator, a Bulk Acoustic Wave (BAW) Resonator, or a Film Bulk Acoustic Resonator (FBAR). Here, the series arm resonators s1 and s2 and the parallel arm resonator p1 are surface acoustic wave resonators. Thus, the filter 10 can be configured by IDT (inter digital Transducer) electrodes formed on a substrate having piezoelectricity, and therefore a small-sized low-back filter circuit having a high-steepness pass characteristic can be realized. The substrate having piezoelectricity is a substrate having piezoelectricity at least on the surface. The substrate may be a laminate of a film having a piezoelectric thin film on a surface thereof and a different sound velocity from the piezoelectric thin film, a support substrate, and the like. The substrate may be, for example, a laminate including a high-sound-velocity supporting substrate and a piezoelectric film formed on the high-sound-velocity supporting substrate; a laminated body including a high-sound-speed supporting substrate, a low-sound-speed film formed on the high-sound-speed supporting substrate, and a piezoelectric thin film formed on the low-sound-speed film; or a laminate comprising a support substrate, a high-sound-velocity film formed on the support substrate, a low-sound-velocity film formed on the high-sound-velocity film, and a piezoelectric thin film formed on the low-sound-velocity film. The substrate may have piezoelectricity over the entire substrate.

At least one of the series arm resonators s1 and s2 and the parallel arm resonator p1 may be a BAW resonator or an FBAR.

The inductor L1 is a first inductor connected in parallel to the series arm resonators s1 and s 2. Specifically, the inductor L1 is connected between the connection point of the series arm resonator s1 and the input/output terminal 11m and the connection point of the series arm resonator s2 and the matching circuit 14 described later.

The matching circuit 14 is connected between the series arm resonator s2 and the input/output terminal 11 n. The matching circuit 14 may be connected between the series arm resonator s1 and the input/output terminal 11 m.

The series arm resonators s1 and s2 and the inductor L1 form the LC resonant circuit 12. Specifically, the LC resonant circuit 12 is configured by the capacitance components of the two series arm resonators s1 and s2 and the inductor L1.

The series arm resonators s1 and s2 and the parallel arm resonator p1 form a passband of the bandpass filter 13.

Note that, hereinafter, for convenience sake, the LC resonant circuit 12 is not limited to a resonator alone, and a singular point (ideally, a point at which the impedance is 0) at which the combined impedance of the resonator and the inductor is extremely small is referred to as a "resonance point" and the frequency thereof is referred to as a "resonance frequency".

The series arm resonators s1 and s2 and the parallel arm resonator p1 are formed of different chips. In other words, the series arm resonators s1 and s2 are formed by one chip, and the parallel arm resonator p1 is formed by another chip. When there is a large difference between the resonance frequency of the series arm resonators s1 and s2 and the resonance frequency of the parallel arm resonator p1, the characteristic variation can be reduced by forming these resonators from different chips. The series arm resonators s1 and s2 and the parallel arm resonator p1 may be formed by one chip.

[2. harmonic oscillator structure ]

Hereinafter, the configuration of each resonator constituting the filter 10 will be described in more detail with a focus on an arbitrary resonator. Since the other resonators have substantially the same configuration as the arbitrary resonator, detailed description thereof is omitted.

Fig. 2 is an example of a diagram schematically showing the structure of a resonator in the present embodiment, where (a) is a plan view and (b) is a sectional view of (a). Note that the resonator shown in fig. 2 is a resonator for explaining a typical configuration of each resonator constituting the filter 10. Therefore, the number, length, and the like of the electrode fingers of the IDT electrode of each resonator constituting the filter 10 are not limited to those of the IDT electrode shown in the figure. In the figure, the reflectors constituting the resonators are not shown.

As shown in fig. a and b, the resonator includes an IDT electrode 101, a piezoelectric substrate 102 on which the IDT electrode 101 is formed, and a protective layer 103 covering the IDT electrode 101.

As shown in fig. 2 (a), a pair of comb-

tooth electrodes

101a and 101b facing each other and constituting the IDT electrode 101 are formed on the piezoelectric substrate 102. The comb-teeth electrode 101a is composed of a plurality of electrode fingers 110a parallel to each other and a bus bar (busbar) electrode 111a connecting the plurality of electrode fingers 110 a. The comb-teeth electrode 101b includes a plurality of electrode fingers 110b parallel to each other and a bus bar electrode 111b connecting the plurality of electrode fingers 110 b. The plurality of

electrode fingers

110a and 110b are formed along a direction orthogonal to the propagation direction.

As shown in fig. 2 (b), the IDT electrode 101 including the plurality of

electrode fingers

110a and 110b and the

bus bar electrodes

111a and 111b has a laminated structure of the adhesion layer 101g and the main electrode layer 101 h.

The protective layer 103 is formed to cover the comb-

teeth electrodes

101a and 101 b. The protective layer 103 is a layer for protecting the main electrode layer 101h from the external environment, adjusting the frequency-temperature characteristics, improving the moisture resistance, and the like, and is a film mainly composed of silicon dioxide, for example.

In the resonator (surface acoustic wave resonator) configured as described above, the wavelength of the excited elastic wave is defined by design parameters of the IDT electrode 101 and the like. That is, the resonant frequency and the antiresonant frequency of the resonator are defined by design parameters of the IDT electrode 101 and the like. Hereinafter, the design parameters of the IDT electrode 101, that is, the design parameters of the comb-

teeth electrodes

101a and 101b will be described.

The series arm resonators s1 and s2 and the parallel arm resonator p1 may be each formed of a plurality of divided resonators divided in series. This can increase the size of each of the series arm resonators s1 and s2 and the parallel arm resonator p 1. That is, the power consumption of each of the series arm resonators s1 and s2 and the parallel arm resonator p1 can be reduced, and the distortion generated can be suppressed.

[3. Filter characteristics ]

Next, the filter characteristics of the filter 10 according to the present embodiment will be described.

First, the filter characteristics of the band-pass filter 13 will be described.

Fig. 3 is a graph showing the filter characteristics of the band-pass filter 13 according to embodiment 1. In fig. 3, 4, 6, 9, and 12A to 12C, the insertion loss increases toward the lower side of the vertical axis of the graph. Fig. 3 shows the filter characteristic of the band-pass filter 13 which is not affected by the inductor L1 (i.e., is not affected by the LC resonance circuit 12). The series arm resonators s1 and s2 and the parallel arm resonator p1 operate as a notch filter, and the resonance frequency of the parallel arm resonator p1 is lower than the resonance frequency of each of the series arm resonators s1 and s2, thereby forming a passband as shown in the figure. At this time, the attenuation amount of the attenuation band on the lower frequency side than the passband of the bandpass filter 13 is small, and the attenuation characteristic is deteriorated. Next, the pass characteristic of the band-pass filter 13 (i.e., the pass characteristic of the filter 10) when affected by the inductor L1 is as shown in fig. 4.

Fig. 4 is a graph showing the filter characteristics of the filter 10 according to embodiment 1. The anti-resonance frequency of each of the two series arm resonators s1 and s2 and the resonance frequency of the parallel arm resonator p1 are separated from each other by adjusting the design parameters of the IDT electrode 101 of each resonator. In general, in a ladder filter, a passband is formed by setting the resonance frequency of the series arm resonator and the anti-resonance frequency of the parallel arm resonator to substantially the same frequency, but in the present embodiment, the resonance frequency of each of the two series arm resonators s1 and s2 is higher than the anti-resonance frequency of the parallel arm resonator p 1. Specifically, the attenuation pole shown in the B section in fig. 4 (referred to as attenuation pole B) corresponds to the resonance frequency of the parallel arm resonator p1, the attenuation pole shown in the C section (referred to as attenuation pole C) corresponds to the anti-resonance frequency of the series arm resonator s1, and the attenuation pole shown in the D section (referred to as attenuation pole D) corresponds to the anti-resonance frequency of the series arm resonator s 2. The series arm resonators s1 and s2 and the parallel arm resonator p1 operate as a notch filter, and the attenuation pole B forms an attenuation slope on the low frequency side of the passband of the filter 10, and the attenuation poles C and D form an attenuation slope on the high frequency side. The passband of the LC resonant circuit 12 is, for example, a band having a relative bandwidth of 4.5% or more, and spans frequencies corresponding to the attenuation poles B to D. However, the anti-resonance frequency of each of the series arm resonators s1 and s2 and the resonance frequency of the parallel arm resonator p1 are located in the passband, and the passband is locally attenuated in fig. 4. Since the series arm resonators s1 and s2 and the parallel arm resonator p1 are surface acoustic waves, their attenuation slopes are steep. At this time, by separating the attenuation pole B from the attenuation poles C and D (that is, separating the anti-resonance frequencies of the series arm resonators s1 and s2 from the resonance frequency of the parallel arm resonator p1), the filter 10 becomes a band-pass filter having a pass characteristic in which a pass band is a wide band. The wide-band passband is wider than the passband of a filter composed of only elastic wave resonators. For example, the wide-band passband is a band having a relative bandwidth of 4.5% or more, preferably 7.5% or more.

The resonance frequency of the LC resonance circuit 12 is lower than the resonance frequency of the parallel arm resonator p 1. The attenuation pole shown in part a in fig. 4 (referred to as attenuation pole a) corresponds to the resonance frequency of the LC resonance circuit 12. This makes it possible to widen the attenuation band on the lower frequency side than the passband of the filter 10. Further, by adjusting the inductance value of inductor L1, the resonance frequency of LC resonance circuit 12 can be adjusted, and the attenuation pole of LC resonance circuit 12 can be made to be distant from the passband of filter 10.

In recent years, a demultiplexer for separating (demultiplexing) a high-frequency signal for each frequency band is widely used to support Carrier Aggregation (CA). As such a demultiplexer, a multiplexer including a plurality of filters is proposed. In such a multiplexer, one end terminal of each filter is directly connected, or a terminal is commonly connected via a phase shifter or a filter selection switch. Thus, the characteristics of one filter may have an effect on the characteristics of the other filters. Therefore, the characteristic of one filter, which does not become a problem for the one filter itself, may become an important factor that degrades the characteristics of the other filters. Specifically, the attenuation characteristic in the attenuation band on the lower frequency side than the pass band of one filter does not affect the pass characteristic in the pass band of the one filter itself. However, when the frequency of the attenuation band is located in the passband of another filter, if the attenuation amount of the attenuation band is small, it becomes an important factor to deteriorate the transmission characteristic in the passband of the other filter.

As shown in fig. 4, the filter 10 has attenuation characteristics in which, for example, a middle band (1710 to 2200MHz) on the lower frequency side of the passband is used as an attenuation band. For example, in the case where one filter of the multiplexer is the filter 10 and the other filter is a filter having the intermediate band as a pass band, when the attenuation amount in the attenuation band of the filter 10 is small, the pass characteristic in the pass band of the other filter may be deteriorated. However, the attenuation pole a corresponding to the resonance frequency of the LC resonant circuit 12 increases the attenuation amount of the attenuation band on the low frequency side of the passband of the filter 10 in a wide range. Therefore, deterioration of the transmission characteristics of the other filters can be suppressed.

Further, a filter having a different configuration from the filter 10 can realize a bandpass filter characteristic having a wide passband. Here, as comparative example 1, a filter 100 as a band-pass filter having a wide passband will be described.

Fig. 5 is a circuit configuration diagram of the filter 100 according to comparative example 1. As shown in the figure, the filter 100 is composed of ladder filters 200 and 300 connected in parallel with each other. The filter 200 includes series arm resonators s21 to s23 and parallel arm resonators p21 and p22, and the filter 300 includes series arm resonators s31 to s33 and parallel arm resonators p31 and p 32. These resonators are, for example, surface acoustic wave resonators.

Fig. 6 is a graph showing filter characteristics of the filter 10 according to embodiment 1 and the filter 100 according to the comparative example. The characteristics of the filter 10 are shown in solid lines and the characteristics of the filter 100 are shown in dashed lines. In general, a filter using a surface acoustic wave resonator, in which a passband is formed by setting a resonance frequency of a series arm resonator and an anti-resonance frequency of a parallel arm resonator to substantially the same frequency, has a relative bandwidth of, for example, 3 to 4%. Accordingly, by using a plurality of filters having different pass bands, as in the filter 100, a band-pass filter characteristic having a wide pass band can be realized. For example, the filter 200 has a filter characteristic with a Band40 (2300-2400 MHz) as a passband, and the filter 300 has a filter characteristic with a Band41 (2496-2690 MHz) as a passband. The filter characteristic of the filter 100 is a composite characteristic of the

filters

200 and 300. However, even when a band-pass filter characteristic in which a passband is wide is realized by using a plurality of filters, it is found that a passband with a small loss as in the filter 10 cannot be realized as shown in fig. 6. Further, it is found that the filter 100 cannot significantly attenuate the attenuation of the attenuation band on the low frequency side of the passband in a wide frequency band.

In the filter 10 of the present embodiment, a high-frequency signal leaks to the inductor L1. That is, the high-frequency signals flowing through the series arm resonators s1 and s2 and the parallel arm resonator p1 are reduced. That is, the power consumption of these resonators is reduced, and the distortion can be suppressed.

Fig. 7 is a graph showing characteristics of third-order intermodulation distortion (hereinafter referred to as IMD3) in the filter 10 according to embodiment 1 and the filter 100 according to the comparative example. In fig. 7, the IMD3 characteristics are better as the ordinate of the graph is lower. Specifically, the figure is a graph showing IMD3 characteristics of Band 7. In the filter 100, almost all of the high-frequency signal flows through the resonator as in the filter 10, and therefore power consumption in the resonator increases. Therefore, as shown in fig. 7, it can be seen that the IMD3 characteristics of the filter 10 are improved.

As described above, the filter 10 can realize a bandpass filter characteristic having a wide passband and a smaller loss than the filter 100 according to comparative example 1.

Further, according to the configuration of the matching circuit 14, the attenuation amount of a predetermined frequency band of the filter 10 can be increased, and the transmission characteristic of another filter having the same frequency band as the predetermined frequency band as a pass band can be improved.

Fig. 8A to 8I are circuit configuration diagrams showing an example of the configuration of the matching circuit 14.

As shown in fig. 8A, the matching circuit 14 may be an inductor L2 connected between the input/output terminal 11m and the input/output terminal 11n and the ground. Inductor L2 is an example of a second inductor. By adjusting the circuit parameters in such a configuration, the matching circuit 14 can function as a filter for attenuating a low frequency band (699 MHz-960), for example. Therefore, the pass characteristics of other filters having a low frequency band as a pass band can be improved.

As shown in fig. 8B, the matching circuit 14 may be an inductor L3 connected in series between the input/output terminal 11m and the input/output terminal 11 n. Inductor L3 is an example of a third inductor. By adjusting the circuit parameters in such a configuration, the matching circuit 14 can function as a filter for attenuating a 5GHz band, for example. Therefore, the transmission characteristics of other filters having the 5GHz band as the pass band can be improved.

The matching circuit 14 may be a capacitor C1 connected between the input/output terminal 11m and the input/output terminal 11n and the ground as shown in fig. 8C, or may be a capacitor C2 connected in series between the input/output terminal 11m and the input/output terminal 11n as shown in fig. 8D.

The matching circuit 14 may be a pi-type circuit including the capacitor C3, the inductors L4, and L5 as shown in fig. 8E, or may be a T-type circuit including the capacitor C4, the inductors L6, and L7 as shown in fig. 8F.

The matching circuit 14 may be a series resonant circuit including a capacitor C5 and an inductor L8 as shown in fig. 8G, or may be a parallel resonant circuit including a capacitor C6 and an inductor L9 as shown in fig. 8H.

As shown in fig. 8I, the matching circuit 14 may be a circuit including a capacitor C7 and an inductor L10.

By configuring the matching circuit 14 and adjusting the circuit parameters as shown in fig. 8A to 8I, the attenuation of a predetermined frequency band of the filter 10 can be increased, and the transmission characteristics of another filter having the same frequency band as the predetermined frequency band as a pass band can be improved.

[4. piezoelectric Material and cut Angle ]

Next, the relationship between the piezoelectric material and the cut angle of the piezoelectric layer in the substrate having the piezoelectric layer constituting the series arm resonators s1 and s2 and the parallel arm resonator p1 and the pass characteristic of the filter 10 will be described.

The parallel arm resonator p1 and the series arm resonators s1 and s2 are each composed of a substrate having a piezoelectric layer and an IDT electrode formed on the substrate. Here, the filter of example 1 in which the piezoelectric materials constituting the piezoelectric layers of the series arm resonators s1 and s2 and the parallel arm resonator p1 are different from each other and the filter of comparative example 2 in which the piezoelectric materials are the same will be described. In comparative example 2, LN love waves were used for the parallel arm resonator p1 and the series arm resonators s1 and s2, respectively, and in example 1, LN rayleigh waves were used for the parallel arm resonator p1 and LN love waves were used for the series arm resonators s1 and s2, respectively.

Fig. 9 is a graph showing filter characteristics of the filter according to example 1 and the filter according to comparative example 2. In fig. 9, the characteristics of the filter according to example 1 are shown by solid lines, and the characteristics of the filter according to comparative example 2 are shown by broken lines. Fig. 10 is a graph showing resonator characteristics of the parallel arm resonator p1 according to example 1 and the parallel arm resonator p1 according to comparative example 2. Fig. 10 shows the resonance characteristics of the parallel arm resonator p1 according to example 1 as a solid line, and shows the resonance characteristics of the parallel arm resonator p1 according to comparative example 2 as a broken line. In fig. 10, the return loss is set to be smaller as the vertical axis of the graph is lower.

For example, in the case where the piezoelectric materials are the same as in comparative example 2, an unnecessary wave (bulk wave) in which the material is an important factor is generated as compared with the case where the piezoelectric materials are different as in example 1, and the loss of the pass band of the filter becomes large. For example, as shown in a portion in fig. 9, it is found that the loss is greatly increased in the vicinity of 2.69GHz in the passband. This is because, as shown in part a of fig. 10, in example 1, the parallel arm resonator p1 is a piezoelectric material different from the series arm resonators s1 and s2, and therefore the return loss is large near 2.69GHz and is in an ideal state close to 0dB, for example, whereas in comparative example 2, the parallel arm resonator p1 is the same piezoelectric material as the series arm resonators s1 and s2, and therefore the return loss is small near 2.69GHz and is far from negative 3dB, for example, from 0 dB. This is an influence caused by generation of an unnecessary wave (bulk wave).

In this way, by making the piezoelectric materials constituting the piezoelectric layers of the parallel arm resonator p1 and the series arm resonators s1 and s21 different from each other, the loss of the passband of the filter 10 can be suppressed.

In addition, similar effects can be achieved by making the respective cut angles of the piezoelectric layers different in the substrates having the piezoelectric layers constituting the series arm resonators s1 and s2 and the parallel arm resonator p 1. That is, when the respective cut angles are the same, an unnecessary wave (bulk wave) whose cut angle is an important factor is generated, and the loss of the passband of the filter becomes larger than when the cut angles are different.

[5. Effect ]

As described above, in the filter 10 (filter device) according to embodiment 1, the two series arm resonators s1 and s2 and the inductor L1 (first inductor) form the LC resonant circuit 12 having a wide passband. Further, the anti-resonance frequency of each of the two series arm resonators s1 and s2 and the resonance frequency of the parallel arm resonator p1 are located in the passband of the LC resonance circuit 12, and thus each resonator operates as a notch filter to locally attenuate the passband of the LC resonance circuit 12. At this time, since the anti-resonance frequency of each of the two series arm resonators s1 and s2 is higher than the resonance frequency of the parallel arm resonator p1, the parallel arm resonator p1 forms an attenuation slope on the low frequency side of the passband of the filter 10, and the two series arm resonators s1 and s2 form an attenuation slope on the high frequency side of the passband. Therefore, by separating the anti-resonance frequency of each of the two series arm resonators s1 and s2 from the resonance frequency of the parallel arm resonator, the passband can be made wide. Further, the matching circuit 14 can reduce the loss of the passband. Therefore, a bandpass filter characteristic having a wide passband and a low loss can be realized.

Further, since the resonance frequency of the LC resonance circuit 12 is lower than the resonance frequency of the parallel arm resonator p1, the attenuation band on the low frequency side of the passband of the filter 10 can be widened, and the attenuation can be increased.

Further, depending on the circuit configuration of the matching circuit 14, for example, the matching circuit 14 can be made to function as a filter for attenuating a low frequency band (699 MHz-960), or as a filter for attenuating a 5GHz band.

Further, the loss of the passband of the filter 10 can be suppressed by making the piezoelectric materials or the cut angles of the piezoelectric layers different in the substrate having the piezoelectric layers constituting the series arm resonators s1 and s2 and the parallel arm resonator p 1.

(embodiment mode 2)

The filter 10 (filter device) described in embodiment 1 can be applied to a multiplexer, a high-frequency front-end circuit, and a communication device. In the present embodiment, description will be given mainly on a multiplexer including a plurality of filters including at least one filter 10 described in embodiment 1. In the multiplexer, the input terminals or the output terminals of the plurality of filters are directly or indirectly connected to the common terminal.

Fig. 11 is a configuration diagram of the multiplexer 40 and its peripheral circuits according to embodiment 2. The figure shows a high frequency front-end circuit 70 with a multiplexer 40, an antenna element ANT, and an RF signal processing circuit (RFIC) 80. The high frequency front end circuit 70 and the RFIC80 constitute a communication device 90. The antenna element ANT, the high-frequency front-end circuit 70, and the RFIC80 are disposed in the front-end of a mobile phone corresponding to, for example, a multi-mode/multi-band.

The antenna element ANT is an antenna for transmitting and receiving a high-frequency signal, and is compatible with multiple frequency bands, for example, according to a communication standard such as LTE. The antenna element ANT may not correspond to all the frequency bands of the communication device 90, and may correspond to only the frequency bands of the low-band group or the high-band group, for example. In addition, the antenna element ANT may be incorporated in the communication device 90.

The high frequency front end circuit 70 is a circuit that transmits a high frequency signal between the antenna element ANT and the RFIC 80. Specifically, the high-frequency front-end circuit 70 passes a high-frequency signal (here, a high-frequency reception signal) received by the antenna element ANT to the RFIC80 via a reception-side signal path.

The high-frequency front-end circuit 70 includes a multiplexer 40, a switch 50, and an amplifier circuit 60.

The multiplexer 40 includes three filters, i.e., the filter 10, the filter 20, and the duplexer (diplexer)30 according to embodiment 1, as a plurality of filters. The multiplexer 40 is compatible with, for example, so-called CA for simultaneously transmitting and receiving signals of a plurality of frequency bands corresponding to the plurality of filters. The filter 20 is a band elimination filter in the present embodiment, and is another filter with respect to the filter 10, and is formed of, for example, a surface acoustic wave resonator. The duplexer 30 includes a high-pass filter 30A and a low-pass filter 30B (low-pass filter), and these filters are formed of, for example, LC filters. The high-pass filter 30A and the low-pass filter 30B have their respective terminals at one end commonly terminated and connected to the antenna element ANT. The filter 20 is connected to the input/output terminal 11m to which the filter 10 is connected. That is, the filter 10 and the filter 20 are commonly terminated at one end by the input/output terminal 11m, and are connected to the other end of the high-pass filter 30A. By connecting the filters included in the multiplexer 40 in this manner, a triplexer is formed as the multiplexer 40.

The passband of the low pass filter 30B is suitable for the low band (699-960 MHz), and the passband of the high pass filter 30A is suitable for at least the middle band and the high band (1710-2690 MHz).

The passband of the filter 10 is adapted for the high frequency band (2300- & 2690MHz), for example. The frequency of the passband of the filter 20 is different from that of the filter 10, and the passband of the filter 20 is suitable for the middle band (1710-. Specifically, the filter 20 (band rejection filter) has an attenuation band overlapping with the passband of the filter 10, and the passband of the filter 10 is different from the passband of the filter 20 because the low frequency side of the attenuation band is the passband. The attenuation band of the filter 20 is a high frequency band (2300-.

According to the multiplexer 40, since the filter 10 described above is provided, a filter characteristic with a small loss can be realized.

The other end terminal of low-pass filter 30B, the other end terminal of filter 10, and the other end terminal of filter 20 are connected to switch 50, respectively.

The switch 50 is connected to the multiplexer 40, and connects signal paths corresponding to a plurality of frequency bands (here, a low frequency band, a middle frequency band, and a high frequency band) having different frequency bands to the amplifier circuit 60 according to a control signal from a control unit (not shown).

The amplifier circuit 60 is, for example, a low noise amplifier connected to the multiplexer 40 via the switch 50, and amplifies the power of the high frequency reception signal received by the antenna element ANT.

The RFIC80 is an RF signal processing circuit that processes a high-frequency signal transmitted and received by the antenna element ANT. Specifically, the RFIC80 performs signal processing on a high-frequency signal (here, a high-frequency reception signal) input from the antenna element ANT via the reception-side signal path of the high-frequency front-end circuit 70 by down-conversion (down-convert) or the like, and outputs the reception signal generated by the signal processing to a baseband signal processing circuit (not shown).

Next, the passing characteristics of the signal paths corresponding to a plurality of bands (low band, intermediate band, and high band) having different frequency bands in the multiplexer 40 will be described.

Fig. 12A is a graph showing the passing characteristics of the signal path corresponding to the high frequency band of the multiplexer 40 according to embodiment 2. Fig. 12B is a graph showing the passing characteristics of the signal path corresponding to the intermediate frequency band of the multiplexer 40 according to embodiment 2. Fig. 12C is a graph showing the passing characteristics of the signal path corresponding to the low band of the multiplexer 40 according to embodiment 2. The signal path corresponding to the high band is a signal path passing through the high pass filter 30A and the filter 10, the signal path corresponding to the middle band is a signal path passing through the high pass filter 30A and the filter 20, and the signal path corresponding to the low band is a signal path passing through the low pass filter 30B.

As shown in fig. 12A and 12B, it is understood that the passband of the signal path corresponding to the high frequency band and the attenuation band of the signal path corresponding to the intermediate frequency band overlap in 2300-2690 MHz. In addition, since the resonance frequency of the LC resonance circuit 12 of the filter 10 is located in the pass band of the filter 20, the attenuation band of the signal path corresponding to the high band and the pass band of the signal path corresponding to the middle band are repeated in 1710-. The resonance frequency of the LC resonance circuit 12 is located near the center frequency of the passband of the filter 20. The resonance frequency of the LC resonance circuit 12 is preferably located on the lower frequency side of the passband of the filter 20 than the center frequency. As a result, the resonance point of the LC resonance circuit 12 is located far from the passband of the filter 10, and the passband of the filter 10 is less likely to be affected by the resonance point, so that loss in the passband can be suppressed.

As shown in fig. 12C, it is understood that the passband of the signal path corresponding to the low band is a different band from the passband of the signal path corresponding to the high band and the passband of the signal path corresponding to the intermediate band, and that the attenuation band on the higher frequency side than the passband of the signal path corresponding to the low band overlaps with the passband of the signal path corresponding to the high band and the passband of the signal path corresponding to the intermediate band.

In this way, in the multiplexer 40, the passband of the signal path corresponding to the high band is located outside the respective passbands of the signal paths corresponding to the intermediate band and the low band, the passband of the signal path corresponding to the intermediate band is located outside the respective passbands of the signal paths corresponding to the high band and the low band, and the passband of the signal path corresponding to the low band is located outside the respective passbands of the signal paths corresponding to the high band and the intermediate band, so that it is possible to cope with so-called CA in which a plurality of bands are transmitted and received simultaneously.

(other embodiments)

The filter device and the multiplexer according to the embodiments of the present invention have been described above with reference to embodiments 1 and 2, but the present invention is not limited to the above embodiments. Other embodiments that are realized by combining arbitrary constituent elements in the above-described embodiments, modified examples obtained by implementing various modifications that will occur to those skilled in the art to the above-described embodiments without departing from the spirit of the present invention, and various devices incorporating the filter device and the multiplexer according to the present invention are also included in the present invention.

For example, the high-frequency front-end circuit 70 and the communication device 90 including the high-frequency front-end circuit 70 and the RFIC80(RF signal processing circuit) are also included in the present invention.

For example, in the above-described embodiment, the filter 10 includes two series arm resonators s1 and s2, but may include three or more series arm resonators.

For example, although the filter 10 includes one parallel arm resonator p1 in the above embodiment, two or more parallel arm resonators may be provided.

For example, although the high frequency front end circuit 70 has a reception side signal path in embodiment 2, it may have a transmission side signal path, and may transmit a high frequency signal (here, a high frequency transmission signal) output from the RFIC80 to the antenna element ANT via the transmission side signal path. In this case, the RFIC80 may perform signal processing on the transmission signal input from the baseband signal processing circuit by up-conversion or the like, and output the high-frequency signal (here, the high-frequency transmission signal) generated by the signal processing to the transmission-side signal path of the high-frequency front-end circuit 70, and the amplifier circuit 60 may be a power amplifier that power-amplifies the high-frequency transmission signal output from the RFIC 80.

For example, in embodiment 2, the multiplexer 40 is a triplexer composed of three filters, but may be a duplexer composed of two filters, a quadruplexer composed of four filters, or the like as long as the filter 10 is provided.

For example, in embodiment 2, the high-frequency front-end circuit 70 includes one switch 50 and one amplifier circuit 60, but may include a plurality of switches. The high-frequency front-end circuit 70 may not include both the switch 50 and the amplifier circuit 60.

Industrial applicability of the invention

The present invention is widely applicable to communication devices such as mobile phones as a filter, a multiplexer, a front-end circuit, and a communication apparatus applicable to a multiband system.

Description of the reference numerals

10 filters (filter devices), 20 filters (other filters), 11m input/output terminals (first terminals), 11n input/output terminals (second terminals), 12 LC resonance circuits, 13 band pass filters, 14 matching circuits, 30 duplexers, 30A high pass filters, 30B low pass filters, 40 multiplexers, 50 switches, 60 amplification circuits, 70 high frequency front end circuits, 80 RFIC (RF signal processing circuits), 90 communication devices, 100, 200, 300 filters, 101 IDT electrodes, 101a, 101B comb electrodes, 101g adhesion layers, 101h main electrode layers, 102 piezoelectric substrates, 103 protective layers, 110A, 110B electrode fingers, 111a, 111B bus electrodes, s-s series resonance arms, p, 102 piezoelectric substrates, p31, p32 … parallel arm resonators, C1-C7 … capacitors, L1 … inductors (first inductors), L2 … inductors (second inductors), L3 … inductors (third inductors), L4-L10 … inductors, and ANT … antenna elements.

Claims

1. A filter device is provided with:

a first series arm resonator provided on a first terminal side and a second series arm resonator provided on a second terminal side, the first series arm resonator being connected in series between the first terminal and the second terminal;

a parallel arm resonator connected between a series arm between the first series arm resonator and the second series arm resonator and a ground;

a first inductor connected in parallel to the first series arm resonator and the second series arm resonator; and

a matching circuit connected between the second series arm resonator and a second terminal or between the first series arm resonator and the first terminal,

the first series arm resonator, the second series arm resonator, and the parallel arm resonator constitute a passband of a bandpass filter,

the first series arm resonator, the second series arm resonator, and the first inductor form an LC resonant circuit,

the anti-resonance frequency of each of the first series arm resonator and the second series arm resonator and the resonance frequency of the parallel arm resonator are located in a pass band of the LC resonant circuit,

the resonance frequency of the LC resonance circuit is lower than the resonance frequency of the parallel arm resonator.

2. The filter arrangement of claim 1,

the resonance frequency of the parallel arm resonator is lower than the resonance frequency of each of the first series arm resonator and the second series arm resonator.

3. The filter arrangement according to claim 1 or 2,

the matching circuit is a second inductor connected between the first terminal and the second terminal and ground.

4. The filter arrangement according to claim 1 or 2,

the matching circuit is a third inductor connected in series between the first terminal and the second terminal.

5. The filter arrangement according to claim 1 or 2,

the parallel arm resonator, the first series arm resonator, and the second series arm resonator are each composed of a substrate having a piezoelectric layer and an IDT electrode formed on the substrate,

the piezoelectric material constituting the piezoelectric layer of the parallel arm resonator is different from the piezoelectric material constituting the piezoelectric layers of the first series arm resonator and the second series arm resonator.

6. The filter arrangement according to claim 1 or 2,

the cut angle of the piezoelectric layer constituting the parallel arm resonator is different from the cut angles of the piezoelectric layers constituting the first series arm resonator and the second series arm resonator.

7. The filter arrangement according to claim 1 or 2,

at least one of the parallel arm resonator, the first series arm resonator, and the second series arm resonator is a bulk acoustic wave resonator or a thin film bulk acoustic wave resonator.

8. A multiplexer, wherein,

a plurality of filters each comprising at least one filter device according to any one of claims 1 to 7,

the input terminals or the output terminals of the plurality of filters are directly or indirectly connected to a common terminal.

9. The multiplexer of claim 8,

the plurality of filters are two filters.

10. The multiplexer of claim 8,

the plurality of filters is three filters.

11. The multiplexer of claim 8,

the plurality of filters is four filters.

12. A multiplexer according to any one of claims 8 to 11,

the plurality of filters include another filter connected to the first terminal and having a passband of a frequency different from that of the filter device,

the resonance frequency of the LC resonance circuit is located in the pass band of the other filter.

13. The multiplexer of claim 12, wherein,

the resonance frequency of the LC resonance circuit is located on the lower frequency side than the center frequency of the passband of the other filter.

14. The multiplexer of claim 12, wherein,

the passband of the filter arrangement described above is adapted to the high frequency band,

the passband of the other filters described above is adapted to the mid-band.

15. A multiplexer according to any one of claims 8 to 11, 13,

the plurality of filters includes a low pass filter.

16. The multiplexer of claim 15, wherein,

the passband of the low pass filter is adapted to the low frequency band.

17. The multiplexer of claim 15, wherein,

the low-pass filter is an LC filter.

18. A multiplexer according to any one of claims 8 to 11, 13 and 16,

and simultaneously transmitting and receiving signals of a plurality of frequency bands corresponding to the plurality of filters.

19. A high-frequency front-end circuit, comprising:

a multiplexer as claimed in any one of claims 8 to 18; and

and a switch connected to the multiplexer.

20. A high-frequency front-end circuit, comprising:

a multiplexer as claimed in any one of claims 8 to 18; and

and an amplifying circuit connected to the multiplexer.

21. A communication device is provided with:

an RF signal processing circuit for processing the high frequency signal transmitted and received by the antenna element; and

the high frequency front-end circuit according to claim 19 or 20, which transmits the high frequency signal between the antenna element and the RF signal processing circuit.